AND KEL'TILIA OF NOETII AMElilCA. 



267 



and the cranium is ^ eiy difterently constrncted ; in Oestscei^halus it is much as in 

 Ptyonius and Lepterjjeton. The characters then arc as follows : 



Form slender and snake-like; caudal vertebras with dilated and sculptured neural 

 and haemal spines. Cranium lanceolate. Teeth numerous, of nearly equal size. No 

 pectoral shields ; abdomen protected by very numerous bristle-like rods, which con- 

 verge forwards ; scales none. A pair of weak posterior limbs ; branchihyal bones 

 present. 



In the only well-preserved species, the cephalic bones exhibit no sculpture from 

 the parietal region forward. The angles of the mandibles are pi'olonged backwards 

 as in Ajjciteoti and the Anura, and the well developed ribs commence but a short dis- 

 tance behind the head. The vertebrae are slender and furnished with well developed 

 diapophyses. The neural spines of the dorsal vertebrae in (). remex are flattened and 

 antero-posteriorly expanded and weakly grooved to their superior margin. 



The character which separates this genera from Ptyonius is the absence of the 

 three usual pectoral shields. In two specimens the pectoral region is presented, and 

 no trace of the shield appears ; on the contrary the .ventral armature of bristles or 

 rods extends to the head. 



A pair of symmetrical bones, whose impressions are seen posterior to the occi- 

 pital bone, I once thought might belong to rudimental limbs. They however appear 

 to be the elements of the second or third branchial haemal arch ; the first or haemal is 

 followed by a second element which is probably the inferior pleural segment of the 

 arch. A third piece follows, which is the superior pleural element of the same. The 

 other branchial arches are lost, but some impressions are visible. 



Before I was fully acquainted with the structure in this genus, I referred some 

 of the species to Scmrojdeura, which is quite distinct. The name is from Ohno', a 

 javelin or dart, in allusion to the form of the head. My friend, Dr. Benjamin H. 

 Coates, informs me that this Greek word retains the dieresis in composition, and 

 should not be spelled with a dipthong. 



I am acquainted with one species from more or less completely preserved skele- 

 tons, with portions or wholes of crania, and another species from cranial remains alone. 



They may be distinguished as follows : 



I. Vertebrae elongate ; fan-like caudal processes narrower. Size large; mandi- 

 bular teeth of unequal lengths, with the apices turned backwards. O. eemex. 



II. Species only known from ci'anial bones with teeth ; teeth equal, erect, with 

 acute conic apices, eleven in .005' m. O. rectidens. 



